1. Field of the Invention
The invention relates to etching process for decreasing mask defect, and more particularly, to etching process which can completely clean a photoresist.
2. Description of the Prior Art
Along with continuously reducing line widths of semiconductor elements, the size of each element of MOS transistors continues to be miniaturized. However, exposure machine, etching machine, and photosensitive material limits the line widths of a semiconductor element so that the development of smaller line widths experiences a bottleneck, especially in the same etching reaction chamber named an in-situ etching process. Therefore, it is important to determine how to decrease a mask defect and improve etching accuracy in the latter etching process.
Please to refer to FIG. 1 and FIG. 2 that are schematic diagrams for defining the gate pattern of a MOS transistor according to prior art. As shown in FIG. 1, a gate oxide layer 12 is formed on a silicon substrate 10, and a doped polysilicon layer 14, a silicon nitride compound mask 16, and a bottom anti-reflection coating (BARC) layer 18 are sequentially formed on the gate oxide layer 12. Finally, a photoresist layer 20 is formed on the BARC 18.
A photolithographic process is performed to define the gate pattern on the photoresist layer 20. Then, an anisotropic etching process is performed, such as utilizing dry etching to remove the BARC 18 and portions of the mask 16 not covered by the patterned photoresist layer 20 to transfer the pattern from the photoresist layer 20 to the mask 16. Employing an in-situ etcher or etching system, the photoresist layer 20 is removed. Utilizing the mask 16 as a hard mask in the etching process, the doped polysilicon layer 14 is etched down to the surface of the gate oxide layer 12 to form the polysilicon pattern, as shown in FIG. 2.
However, the above-described prior art method still has shortcomings. When using a smaller than 90 nm process, the above-described in-suit etching process cannot completely remove the photoresist layer. Today's pure O2 strip processes will produce halogenated compound polymers formed by F, HBr, Cl, etc. from the etching mask 16 and the photoresist 20 during the process. The halogenated compound polymers causes hard mask defects in later etching of the doped polysilicon layer 14 and influences the accuracy of the mask 16, seriously affecting the quality of the latter etching process.
Therefore, the applicant proposes a method of reducing mask defects to prevent above-described problems.